1. Field of the Invention
The present invention relates to laminated armour suitable for protection against small calibre kinetic energy rounds and particularly against fragmentation attack, but is also suitable as a containment means in a situation when there is a possibility of fragments being ejected at high speed for example during the operation of aircraft turbo fans.
2. Discussion of Prior Art
The terms "V.sub.50 protection limit" and "merit rating" which are used in the description are defined as follows:
V.sub.50 Protection Limit (m/s)--relates to attack with a particular type of projectile and represents the impact velocity which gives a 50% chance of armour defeat (by any failure mode). ##EQU1## Merit rating provides a normalisation of V.sub.50 results permitting comparison of armours with different areal densities (NB realistic comparison of different armours can only be made using merit rating provided the areal densities are of the same order.) PA1 a. Plugging--in which local through thickness shear failure takes place resulting in a plug of material with a diameter of the same order as that of the projectile being removed from the armour. The plug itself may be ejected with residual kinetic energy and constitute a dangerous secondary projectile. Plugging is a low energy absorption mechanism because little plastic deformation of the armour takes place, and for this reason its avoidance is very desirable; PA1 b. Discing or Scabbing--which involves the ejection of a disc of material spalled from the rear surface of the armour. This is also a low energy failure mechanism and is also to be avoided if possible, as it does not permit the full potential of the armour to be exploited; PA1 c. Segmenting--which involves the formation of radial cracks defining segments of armour which bend rearwards away from the attacking projectile as it passes into the armour. Since this involves a considerable amount of plastic deformation and ductile fracture, this is a higher energy failure mechanism than plugging or discing. PA1 (i) the first part comprises a lamination of first metal sheets each having an average thickness t adhesively bonded by interface layers having a thickness between 0.4 t and 0.9 t and a compressive Young's Modulus measured perpendicular to the layers of below 4 GPa, PA1 (ii) the second part comprises at least one metal sheet which is more ductile than the metal of the first metal sheets.
When attacked by armour piercing rounds or fragments from for example a fragmentation attack bomb, relatively lightweight armour is susceptible to a number of different failure modes. These are:
Dual hardness armour systems have been proposed in the past which incorporate a hard ceramic layer for blunting or fragmenting the projectile on the armour's attack side, backed by a layer containing glass fibre reinforced resin which is designed to absorb the projectile's kinetic energy by deformation. Examples of such armours are described in French patent 823,284 and U.S. Pat. No. 4,131,053. Recently it has been proposed in EP patent 237095 to incorporate a fibre reinforced metal laminate into the armour system described above. All these armour systems are however applique i.e. only suitable for being applied to a structure. They are not suitable for use as structural armours themselves.
Dual ductility structural armours have been proposed in the past which incorporate a hard attack surface layer backed by a ductile spall prevention layer. In order that such armour will not distort under load the rear layer of ductile low strength metal commonly occupies 50% or more of the armour by volume with a consequential reduction in the armour's merit rating.